The present invention relates to an improved high density plasma enhanced chemical vapor deposition method, and more particularly to an improved high density plasma enhanced chemical vapor deposition method for depositing an inter-layer insulator or a passivation film which buries a gap of adjacent interconnections having a small distance.
Multilevel interconnections and inter-layer insulators are essential to increase a density of integration of semiconductor integrated circuits. In order to reduce a parasitic capacitance between different level interconnections and two adjacent interconnections of the same level, silicon dioxide is often used for the inter-layer insulator.
In order to realize the required size reduction, it is of course required to reduce a distance between two adjacent interconnections of the same level. In order to reduce a resistance of the interconnection, it is also required to increase a sectioned area of the interconnection. For those reasons, a high aspect ratio of a gap between two adjacent interconnections of the same level is thus required to both realize the required size reduction and reduce the resistance of the interconnection, wherein an aspect ratio is defined to be a ratio of a thickness of an interconnection layer or a height of the interconnection layer to a distance between the two adjacent interconnections of the same level. The interconnection layers are required to be buried within an insulating layer such as an inter-layer insulator or a passivation layer. This means that it is required to fill the insulating layer into the high aspect ratio gap between two adjacent interconnections of the same level.
A plasma enhanced chemical vapor deposition method for deposition of an insulating film has been in development wherein a high frequency power is applied to a silicon substrate. This plasma enhanced chemical vapor deposition method utilizes a dependency of a sputtering etching rate of argon ions upon an oblique angle, wherein the sputtering etching rate is higher efficiency to a sloped portion. This makes it possible to use the argon ion sputtering etching method to remove the insulation film on a comer of a step-shaped portion or a rectangular-shaped portion, so that the insulation film is filled into the narrow gap between the two adjacent interconnections of the same level at the same time when the insulating film is deposited. The deposition and the sputtering processes are simultaneously carried out. If a ratio of the local sputtering rate to the local deposition rate is high, it is possible to realize a required complete burying of the insulation film into an extremely narrow gap between two adjacent interconnections of the same level. In this case, however, the net deposition rate defined by a subtraction of the local sputtering rate from the local deposition rate is low. A sufficiently large net-deposition rate is necessary in order to realize the required complete burying of the insulation film into the extremely narrow gap between two adjacent interconnections of the same level.
An electron cyclotron resonance plasma enhanced chemical vapor deposition method is typical of the high density plasma enhanced chemical vapor deposition methods. These high density plasma enhanced chemical vapor deposition methods may form a high density plasma having an electron density of about 1xc3x971012(cmxe2x88x923) even under a low pressure of about several tens mTorr. The ions of the plasma under low pressure have a high directivity which permits the deposit of silicon oxide film to bury an extremely narrow gap between two adjacent interconnections of the same level, wherein the extremely narrow gap has an aspect ratio of not less than 1 and a distance between two adjacent interconnections of the same level is not higher than 0.5 micrometers. The other high density plasma enhanced chemical vapor deposition methods are, for example, a helicon wave plasma enhanced chemical vapor deposition method and an inductively coupled plasma enhanced chemical vapor deposition method. Every plasma enhanced chemical vapor deposition method is characterized by a deposition under low pressure in a reaction chamber vacuumed by a turbo molecular pump.
A chemical mechanical polishing method is also available following the above high density plasma chemical vapor deposition method whereby the insulating film is deposited to bury the extremely narrow gap between two adjacent interconnections of the same level before a surface of the deposited insulating film is then planarized.
In International Electron Device Meeting technical Digest, December 1992, pp. 285-288, entitled xe2x80x9cHigh Quality High Rate SiO2 and SiN Room Temperature Formation by Utilizing High Excited Ionsxe2x80x9d, it is disclosed that the electron cyclotron resonance plasma enhanced chemical vapor deposition method is used to evaluate qualities of the deposited insulating films influenced by a difference in frequency of a high frequency power applied to the substrate. If the high frequency power of 400 kHz is applied to the substrate, then a wet etching rate of the silicon nitride film by a buffered fluorine acid is lower than when the high frequency power of 13.56 MHz is applied to the substrate. The fact of the low etching rate of the silicon nitride film deposited by the high density plasma enhanced chemical vapor deposition by applying the high frequency power of 400 kHz to the substrate means that the decreases in frequency of the power to be applied to the substrate for the high density plasma enhanced chemical vapor deposition results in increases in film density and quality of the deposited silicon nitride film. The mechanism of the above phenomenon is as follows. If the power of not so high frequency, for example, about 400 kHz, is applied to the substrate for the high density plasma enhanced chemical vapor deposition, then heavy ions have efficient bombardment with the insulating film. These efficient ion bombardment increases the film density of the insulating film.
In general, if the power of the very high frequency, for example, 13.56 MHz, is applied to the substrate for the high density plasma enhanced chemical vapor deposition, then electrons follow the very high frequency due to their small mass whilst ions having a relatively large mass, for example, argon ions, do not follow the very high frequency. As a result, the ions having a relatively large mass such as argon ions are simply accelerated in direct current by a potential difference between ion sheathes. Namely, under the very high frequency condition, the ions having a relatively large mass such as argon ions are dc-accelerated by a self-bias voltage which corresponds to a potential difference defined by Vpxe2x88x92Vt, wherein Vp is a potential of plasma with reference to the ground potential whilst Vt is a potential of a surface of the substrate with reference to the ground potential. If, however, the power of not so high frequency such as 400 kHz is applied to the substrate for the high density plasma enhanced chemical vapor deposition method, then the ions of a relatively large mass follow the not so high frequency, for which reason positive ions of a relatively large mass such as argon ions are accelerated for every half period so that the accelerated positive ions have collisions with the substrate. Much ion bombardment to the insulation film increases the film density and quality of the insulating film.
In Solid State Technology, April 1990, pp. 139-144, entitled xe2x80x9cIon bombardment: A Determining Factor in Plasma CVDxe2x80x9d, it is disclosed that the ions having a relatively large follow the frequency of not higher than 3MHz.
In the above circumstances, it had been required to develop a novel high density plasma enhanced chemical vapor deposition method free from the above disadvantage and problems.
Accordingly, it is an object of the present invention to provide a novel high density plasma enhanced chemical vapor deposition method free from the above problems.
It is a further object of the present invention to provide a novel high density plasma enhanced chemical vapor deposition method capable of depositing an insulating film having a high quality and a high property.
It is furthermore an object of the present invention to provide a novel high density plasma enhanced chemical vapor deposition method capable of depositing an insulating film keeping an underlying Si/SiO2 interface free from an interface state, where the underlying Si/SiO2 interface has already been formed under the insulating film.
It is a still further object of the present invention to provide a novel high density plasma enhanced chemical vapor deposition method capable of depositing an insulating film at a good gap filling.
It is yet a further object of the present invention to provide a novel high density plasma enhanced chemical vapor deposition method capable of depositing an insulating film which buries an extremely narrow gap of a high aspect ratio between two adjacent interconnections of the same level.
The first present invention provides a first novel high density plasma enhanced chemical vapor deposition method for depositing an insulating such as a silicon dioxide film on a silicon region such as a silicon substrate, wherein the plasma enhanced chemical vapor deposition method includes at least both a first deposition period during which a first power having a first frequency is applied to the silicon region and a second deposition period during which a second power having a second frequency which is lower than the first frequency is applied to the silicon region.
The second present invention provides a second novel method of forming an insulating film, wherein a high density plasma enhanced chemical vapor deposition is carried out to deposit an insulating film such as an SiO2 film on a silicon region such as an Si substrate by applying the silicon region with a power having a frequency which is maintained in the range of not less than 1.8 MHz so as to suppress the formation of any interface state on an Si/SiO2 interface having already been formed under said insulating film.
The third present invention provides a third novel high density plasma enhanced chemical vapor deposition method for depositing an insulating film such as a silicon dioxide film on a silicon region such as a silicon substrate, wherein the plasma enhanced chemical vapor deposition method is carried out by applying the silicon region with a power having a frequency which is maintained in a first high frequency range of not less than 1.8 MHz during at least an initial period of the deposition.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.